The present invention relates to electronically steered phased array antennas and, more particularly, to systems for correcting errors associated with undesirable movement, vibration and flexure thereof.
In electronically steered phased array antennas, the forming and shaping of the radiated and/or received beam is performed by an array of discrete antenna elements in conjunction with phase shifters which insert a specified amount of phase shift into the signal being radiated from and received by each antenna element. The amount of phase shift to be introduced for each discrete antenna element is a function of the desired beam pointing angle and the desired beam shape. Individual phase shift amounts for each phase shifter are calculated by a microcomputer and are communicated to the individual phase shifters.
A state-of-the-art solid state radar transmitter/receiver module (T/R module) combines, on a single integrated circuit board, a phase shifter, a transmit/receive switch (T/R switch), a transmit amplifier, a receive amplifier, and a T/R module controller. An integral antenna element may also reside on or be co-located with the integrated circuit T/R module.
An electronically steered phased array antenna may be constructed with an array of T/R modules and associated antenna elements in which the respective T/R modules are each connected to a data bus which feeds phase delay information to the individual T/R modules.
However, performance of such phased array antennas can be sharply reduced due to unwanted movement, flexure and vibration of the phased array antenna on its platform. This movement, flexure and vibration causes displacement of the antenna elements with respect to one another which in turn causes errors to be introduced into the operation of the antenna array. These errors are particularly pronounced when an antenna array operates at a relatively high microwave frequency such as X-band or higher. Unwanted movement, flexure and vibration causes errors to some degree in all antenna arrays but such errors are most pronounced in antenna arrays having relatively lightweight and flexible back structures, such as where a lightweight antenna array is mounted on an aircraft or other vehicle.
To combat such unwanted movement, flexure and vibration, rigid back structures are presently used to precisely and rigidly support the array of discrete antenna elements and to thereby fix the relative position of each antenna element in order to eliminate flexure across the overall antenna. By rigidly fixing the relative position of each discrete antenna element, the relative position of each antenna element with respect to other elements and with respect to the antenna platform remains constant and need not be compensated for in controlling the phase shift of signals provided to the discrete antenna elements.
However, in modern high resolution radar systems, the antenna flexure tolerances required to maintain acceptable resolution are extremely low. As a result, the back structures required to maintain such low tolerances are quite massive and present numerous design obstacles. For example, these back structures are considerably large and heavy and, in an airborne environment, often require extensive and costly modifications to the host aircraft in order to accommodate them.
It is therefore an object of the present invention to provide an array antenna system that eliminates the need for these massive rigid back structures and still obtain high resolution in an imaging radar system.